Piston & valve. Do they look normal to you?

Heya,

I'm looking at this piston thinking perhaps it looks a tad oily and the stains reach down too far.
Does it look like I need new rings?


Also, cleaning my cylinder head, this valve is #1 exhaust valve. I believe that you should be leaving a carbon crust around the edge of it, but does this look overly filthy to you?


Aand heres #4 intake valve, should I clean this thing up?


Cheers all.

 

Not like I tear into a lot of engines or anything, not my line of work. But that piston doesn't look normal to me. Looks like you may have had bad oil ring or rings/cylinder in general. You should only see carbon build up on the top of the pistons. The valves look to be gunked up as well. Maybe bad valve seals / guides. Especially #4.

Did you do a compression check before tear down? That would have told you a lot. A leak down test all the better yet. What condition are the cylinder bores? You can do some measurements and compare your findings to the service manual. Then go from there on what is required.

 

From the looks of things, ... you were definitely blowing Oil.

The Exhaust Valves condition would generally confirm that.

There are several reasons why Oil gets beyond the Oil Control Rings:

High Miles without sufficient maintenance. Old and highly contaminated Oil.
Oil Control Rings and Ports contaminated with Gunk ... (which presents what you show in photos).

Worn-down Cylinder resulting from the above. The Hole isn't getting enough of a Clean-oil sheen left behind to prevent premature wear. (Or just High miles wear requiring Over-sized Rings after Cylinder Honing.

Examine the Hole.
Look for scratches or gouging.
Measure the Hole with an "Inside-Micrometer".

Do a "Ring Gap" Test.
Place a Compression Ring LEVEL within the Cylinder.
Take an accurate measurement of the GAP in the Ring.

If the gap is too wide out-of-specs ... you have to use over-sized Rings or Over-sized Pistons after Honing the Cylinder.

 

I have to agree with Rick; and take it a step further:

A lot of the oil on the valves themselves could be due to bad valve stem seals as well, and since you have the valves out, I assume you'll be replacing those anyway. Be sure to check the valve spring free length against spec, and pay attention to the coil-direction orientation of the valve springs when you reassemble.

As Rick said, the decision on the pistons and rings will depend on the condition and measurements of the cylinders.

 

Ok so, I've tried measuring my cylinders with my digital caliper but the damn thing wont give me a consistent reading.

Cylinders look pretty good, lovely caramel colour, no scratches, sort of blotchy discolouration which might have been when I washed them (carbon ring at top is intact).

I did the piston ring gap check tho (spec = 0.15 - 0.35):
#piston upper compression ring / lower compression ring
#1 0.20 / 0.30
#2 0.20 / 0.22?
#3 0.30 / 0.24
#4 0.40 / 0.24

Now I've removed the valves and I can see what are probably the valve stem seals but I have no idea how to get them out, and my Clymer says its a job for Yamaha.

 

Get a real book.

The cylinders need to be measured in three places; top, middle, bottom, using a bore gauge. Then (AFTER honing,) you measure them again, measure the pistons and compare the piston-to-cylinder differences (gap) to the published spec. Then do the ring gap test again to determine if you can use stock rings; and check the ring-to-piston "land" (the groove the rings fit in) gap against spec.

THEN AND ONLY THEN will you know if you can re-use those pistons, or need new stock pistons, or need to try to find oversized pistons/rings. From the looks of things you're gonna be OK; but don't buy any parts until you're sure.

The valve stem seals are little "rubber" caps that go on top of the valve guides. You can generally grab them with needle nose pliers and rip them out.




The valves, head, pistons and cylinders all need to be throughly cleaned. The valves will need to be (at the very least) lapped; the valve seats may need "cutting" (best left to a pro.) Any seriously pitted valves should be replaced. Here in the States, it's generally easier to take the head to a qualified 'jobber' that does motorcycle and foreign car heads and pay a couple hundred $$$ to get the job done right.

If you've never serviced a head before, it CAN be done on a DIY basis, but it's a big hassle and will require a few specialized (yet inexpensive) tools. And you're gonna have to learn a whole bunch of stuff in the process. Having done both, I just take them somewhere these days.

A bit of advice: get a factory book. The Clymer is woefully lacking when it comes to this level of repairs.

 

Are you using a telescoping digital bore gage? I used a manual insize (bore gage) telescoping gage, then used a micrometer to measure it. When I measured mine, I measured each cylinder at three different points in the height of the cylinder. Two measurements at each height (perpendicular to each other). I then compared it to the specs in my service manual to see if each cylinder is within tolerance. You should also measure each piston skirt and see they are in tolerance. As Rick mentioned, check the ring gaps. You can do measurements on your values while you are at it (make sure none are bent, etc..). Would suggest lapping them since you have them out already. Since you have this much work into it, may as well go all the way and check everyhing out.

Edit: Dam Fitz! You type much faster than I do. Sorry for the repetition. If I would have know I would have said, "Yeah, what Fitz said", LOL.

One more Edit: One thing I would suggest is, try to get the Viton type valve seals if available for your model. They handle a much higher temperature.

 

Cheers fellas,
I'm going to buddy up to my local mechanic and see how much he'll charge to measure my bores for me.

re: valve stem oil seals, I've been looking at some wildly varying prices and as far as I can tell, the same seals are used on a number of bikes:
http://www.athenaparts.com/eng/products ... -seals-kit

So the xt125 is one of he bikes that apparently shares this.
Do you guys know any way to verify this before I buy?

also, Wemoto specifies inlet valve seals and exhaust valve seals
whereas other places do not specify.
They look pretty similar to me, ok to buy one kind for all 8 valves?

ALSO
Just had a chat with Sprabuild Brighton. They are deglazing my cylinders for me.
They also measured them up and found them 2 - 2 1/2 thousands of an inch out. which is within spec, (.0004" max) but he reckoned the rings were knackered.
Will get him to re-check after the honing.
I'm also going to get him to weld my frame and lap my valves and pretty much everything. They are my kind of people.

 

Lapping valves is easy enough for you to do yourself though, mate. Its fun if you ask me; makes me feel like a true mechanic! Yes I've done it myself if you were wondering whether I'm making this up. Carry on though with your work, I've been in similar shoes and these guys will help with every step if you just ask. When putting it all back together, don't rush it. Follow every step in the book and repeat the directions twice in your head before moving on. You've got a long ways to go I suspect if your frame needs welded anyways.

 

Might want to consider these as well.

http://www.ebay.co.uk/itm/YAMAHA-XJ550- ... 4602a396d6

Viton material is by DuPont. Will last much longer than the conventional composite rubber. As the list points out, "Viton has far better resistance to high temperatures and petroleum distillates and will maintain their elasticity for many years". And you are getting newly manufactured rubber that has not been sitting away for years.

 

Cheers!
I bought those seals

re: lapping, paying them costs four times as much as buying a lapping kit, which is only 4 quid. but I'll never use the kit again and I might be able to push my luck getting hem to weld tabs for the new seat

re: frame welding, its ok, frame is fine, I'm cutting it up and adding a loop at the end. Was going to learn how to weld and do it myself, but i just dont have enough access to a mig.